1. Field of the Invention
The present invention relates to a gamma reference voltage generating circuit and a flat panel display having the same. In particular, the present invention relates to a gamma reference voltage generating circuit that minimizes voltage fluctuation to output a stable gamma reference voltage, and a flat panel display having the gamma reference voltage generating circuit.
2. Description of the Background
Flat panel displays have been used widely as displays for personal computers, mobile communication terminals, etc. Recently, studies on displays that use light emitting diodes (LED), such as an organic light emitting display (organic EL), are actively underway. Since the organic EL does not require a backlight, which causes the increase in thickness and weight, and it has a high-speed response, it is suitable for reproducing moving images.
FIG. 1 schematically illustrates an example of a conventional organic EL.
Referring to FIG. 1, the organic EL includes a display panel 11, a scan driver 12, and a data driver 13, wherein a plurality of data lines D[1] through D[m] are arranged in a vertical direction and a plurality of scan lines S[1] through S[n] are arranged in a horizontal direction on the display panel 11.
Also, at least one pixel is formed at intersections of the data lines D[1] through D[m] and scan lines S[1] through S[n]. Each pixel includes a pixel circuit 14 therein.
The pixel circuit 14 includes a transistor, a capacitor, and an organic light-emitting device (OLED). In general, the organic EL allows the OLED to emit light by adjusting a voltage between the source and gate of a driving transistor using a data signal supplied from the data driver 13 to flow the corresponding current to the OLED.
The data driver 13 receives a gamma reference voltage and a digital gray-level data signal and converts the digital gray-level data signal into an analog gray-level data signal to drive the display panel.
FIG. 2 is a circuit diagram that illustrates an example of a conventional gamma reference voltage generating circuit.
Referring to FIG. 2, in the conventional gamma reference voltage generating circuit, a plurality of resistors R1 through RN (N is an integer) are connected in series between two supply voltages. A plurality of capacitors C1 through C(N-1) are respectively connected between common nodes that are respectively disposed between pairs of adjacent resistors R1 through RN, and one of the two supply voltages. Generally, one of the supply voltages is a supply voltage Vcc which is a positive high voltage and the other is a ground voltage GND which is a low supply voltage.
The gamma reference voltage generating circuit constructed as described above divides a voltage between the two supply voltages into smaller voltages through the resistors R1 through RN. It then outputs the divided voltages as gamma reference voltages to the data driver 13. However, due to the resistance load of the data driver 13, the resulting gamma reference voltages may become unstable and may fluctuate, for example.
Since an unstable gamma reference voltage may cause a variation in a data signal that is applied to the pixel circuit 14, gray-levels of an image to be displayed may be represented correctly. This problem is particularly significant for data signals with fewer bits that operate at a high speed during digital to analog (D/A) conversion, which deteriorates the picture quality of the organic EL screen.